Machining of materials to create openings or recesses of different shapes is used in the manufacture and repair of a wide range of objects. In applications where the dimensional tolerances, roundness and smoothness of the machined surface are important, special tools are often required, especially when the material to be machined is very hard or otherwise difficult to machine. For example, transfer machines within an automated manufacturing line often require multiple machining heads with a variety of different cutting bits to form rounded openings of the desired profiles. The more different machining heads required in a line transfer machine, the more complex the machine becomes, and the more floor space it requires. As an alternative to multiple machining heads, a single cutting machine can be adapted to receive a variety of different cutting bits. However, when the cutting bit needs to be changed, the processing line must be paused or shut down, resulting in reduced throughput.
In an exemplary application, such cutting tools are used in the repair of the cylinders heads of internal combustion engines to re-establish the high quality seal required for efficient engine performance and fuel consumption. It is well known among vehicle mechanics that valve seats can be machined to remove the outer surface of the seat to expose a smooth and uniform contact surface by a technique commonly referred to as “lapping”. This lapping technique is accomplished by removing the cylinder head from the engine and machining the valve seats with a cutting blade. In most common commercial systems, a valve seat has a profile with three different angles: a throat angle, a valve seat angle, and a top angle. In order to simultaneously cut the different angles, a “three-angle” cutting blade or bit is used. Each cutting edge of the three-angle cutting bit corresponds to one of the valve seat angles to be machined. Three-angle cutting bits vary in size and shape depending on the type of cylinder head valve seat being machined. These three-angle cutting bits are currently used by valve seat and guide manufacturers.
A disadvantage of the lapping technique is the risk of damage to the surface finish from vibration, chattering, or undulation generated by flexion of the cutting bits. This problem develops because certain cylinder head valve seat shapes require a three-angle cutting bit with a long cutting edge. Rotation of this long cutting edge when the edge is in contact with the work surface can create flexions in the cutting bit, especially when the material is difficult to machine, e.g., a very hard material. These flexions generate vibrations, chattering, or undulations which can disrupt contact between the cutting edge and the surface being cut. The skipping blade can damage the surface finish of the valve seat resulting in a machined valve seat that is not acceptable by Original Equipment Manufacturer (OEM) standards.
Another disadvantage of the lapping technique is a decentering phenomenon. As stated above, cutting efforts with a long cutting edge/surface create flexions. These flexions create an unbalanced radial cutting effort which decenters the three-angle cutting blade, also resulting in unacceptable quality.
Still another disadvantage of the lapping technique is the large number of three-angle cutting blades needed to machine different types of valve seats. Each type of engine has a different valve seat profile. Thus, one or more unique three-angle cutting blades may be needed for each type of engine.
Single point cutting heads for use in machining systems are described in U.S. Pat. No. 6,086,293, U.S. Pat. No. 6,382,883, U.S. Pat. No. 6,382,884, U.S. Pat. No. 6,530,727 and U.S. Pat. No. 6,640,410, the disclosures of which are incorporated herein by reference in their entireties. Briefly, these systems utilize a single cutting tip that is mounted on a carriage that moves radially outward and inward as the spindle rotates to cut varying profiles. Such systems incorporate computer controllers in which software is provided to permit the machine operator to design a desired profile, for example, a valve seat in an engine cylinder head. Exemplary software for creating a profile to be machined is described in U.S. Publication No. 2004/0186793, the disclosure of which is incorporated herein by reference. The process of designing the profile must take into consideration any pre-existing topography in the workpiece. Where the surface of the workpiece has pre-existing topography, the operator must provide a rendering of the existing cylinder head profile prior to machining. The desired and pre-existing profiles are then overlaid in the software to determine the difference between the two profiles. The software then generates commands causing the machine to “zig zag” into the material machining only the metal/material that corresponds to the difference between the material's pre-existing profile (, i.e., the “casting”) and the “cut profile” (desired profile). The requirement for such information results in a process that can become fairly difficult, especially when there is a large number of different radii and fairly complex shapes to reproduce. According to the present invention, a device and software combination provides means for measurement of the casting and cut profile area, providing a signal for input into the computer controller for automatically generating the control commands for generating the desired profile in the workpiece.